All you have to do is Click your virtual PC then Settings Buttons. When you reach your settings, click on storage section. and click on the folder shortcut for your drive or CD.
Click the Add button, and look for your Image for your CD which is an ISO, or VDI, VMDK, VHD, and HDD for your virtual device.
Read my tutorial on Mounting a VMware VMDK file in Sun VirtualBox tutorial . It is basically the same for mounting ISO, and other Virtual storage device file types.